ABC15.com

The mysterious bright light spotted in Arizona, California and Nevada was a fragment of a small asteroid between the size of a baseball and a basketball, a NASA official told ABCNews.com.

“It only takes something very, very small to create that light,” said Veronica McGregor, a spokeswoman at NASA’s Jet Propulsion Laboratory in California.

Reports of the fireball, which reportedly traveled east across the western U.S., streamed in on the American Meteor Society’s website Wednesday.

Toni Flint, from Glendale, Ariz., wrote that it was “the most amazing and beautiful sight that I have ever seen” and Judith Withers from Warner Springs, Calif., described the meteor as “one BIG blue fireball with a lighter train moving slowly.”

“It was a ‘holy cow, what was that?’ event,” said Sue from Phoenix.

One of the biggest misconceptions about fireballs is that people assume they are seeing a large object traveling across the sky, said Ed Krupp, director of the Griffith Observatory in Los Angeles.  Not so, he says.

“They are seeing the air that this object is heating,” Krupp said. “It heats up a column of air tremendously as it passes through the atmosphere.”

It’s that heating process that produces different colors.

In videos the meteor appeared white, although some eyewitnesses said the light had a bluish-green tint. To others, it appeared orange.

“The oxygen and the nitrogen at that high altitude will respond to the heating by giving off light,” Krupp said. “It looked greenish at the head where it was the hottest and looked reddish and yellowish as the gasses behind it were cooling.”

The asteroid was so small when it hit the atmosphere that there was never any danger of it doing damage.

“Anything less than 30 meters across when it hits our atmosphere will disintegrate,” McGregor said. “We are looking for objects that are bigger and could pose a risk to Earth.”

Several thousand fireballs occur in the Earth’s atmosphere every day, according to the American Meteor Society. They aren’t spotted, however, because most of these meteors travel over the ocean in unpopulated regions and some occur during the day.

“What is unique for this one is that it happened at night time over a very, very populated area and you have potentially millions of people who saw it,” McGregor said. ”And for us that’s very exciting. It just reminds people how cool space science is. We live in a busy neighborhood in our solar system.”